This invention relates to shock absorbing struts for use upon landing gear, particularly those on aircraft. The shock absorbing struts include a resilient element such as an enclosed quantity of gas which is loaded by a movable wall formed as part of a cylinder telescoping within an additional cylinder to absorb shocks imparted by movement of the landing gear upon landing or taxiing of the aircraft.
In a conventional aircraft shock absorber strut the vertical kinetic energy of an aircraft impacting the runway during landing is absorbed by a hydraulic shock absorber. The absorption of the shock occurs by fluid being forced through an orifice under the pressure generated from the forces created by the landing gear impacting the runway and compressing the shock strut. The function of the shock strut is to spread out the impact shock over the longest possible period of time thereby lowering the level of vertical deceleration to the air frame and producing minimum discomfort to passengers and minimum load on the aircraft structure.
In prior art shock absorber struts this lower level of vertical deceleration has been realized through the utilization of providing a variable damping rate of the shock strut through the use of a variable area orifice through which the fluid passes. This has been accomplished by moving a tapered metering pin of varying diameter into the center of the orifice attached to the moving end of the shock strut. Alternatively, the variation in orifice flow area may be realized by opening or closing a plurality of openings provided in a flow tube. Such prior art apparatus is illustrated in the following U.S. Pat. Nos: 4,007,894, 2,814,482, 3,888,436, 4,291,850, 4,284,255, 4,088,286, 3,991,863, 3,171,546, 3,140,084, 2,735,674, 2,563,518.
Other prior art apparatus has been developed which takes into consideration the differences in the shocks applied to the aircraft landing gear and thus the shock absorbing struts on landing as opposed to taxiing of the aircraft. One form of such a structure includes two different flow paths for the liquid which is displaced by the forces generated while the aircraft is landing or taxiing. A selector valve is operable to direct the displaced liquid selectively through one or the other of these flow paths, responsive to either aircraft landing or aircraft taxiing. Each of the flow paths has a flow restricting means to provide the damping required for the aircraft operational status with the particular flow restricting means being different in each instance. Typical of such devices are those shown in U.S. Pat. Nos. 4,065,078 and 4,004,762.
Yet another shock absorber apparatus includes a piston having a flow path including an automatically adjustable orifice therein to thereby effect the desired damping proportional to the pressures generated within the shock absorber by way of the loads supplied to the aircraft landing gear upon landing or taxiing. The adjustable orifice is adjusted by controlling the impedance to the flow of the damping fluid through the orifice through the utilization of a fluidic vortex valve which utilizes small control jets of high pressure fluid injected tangentially into a circular chamber through which the main flow of hydraulic damping fluid passes. The injected high pressure fluid creates a swirling action in the main fluid flow path thus controlling the rate of flow of the fluid through the control jets is controlled by a servovalve which is in turn controlled by an automatic sensing system keyed to the aircraft's vertical acceleration. Such a structure is disclosed in U.S. Pat. No. 3,743,222.